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Development of a Protocol for Holistic Structural Reliability Assessment of Bridges

The current Load and Resistance Factor Rating (LRFR) American Association of State Highway and Transportation Officials (AASHTO) methodology in the Manual for Bridge Evaluation (MBE) includes the use of two adjustment factors to account for local component condition (&amp;#981;c) and structural system redundancy (&amp;#981;s) for strength limit states. The &amp;#981;c and &amp;#981;s factors have not been utilized extensively in Nebraska, partially to maintain existing load ratings through historic procedures (Allowable Stress Rating, ASR; Load Factor Rating, LFR), but also partially because the available guidance lacks precision in the applicability of the factors and potentially imposes an unfair strength capacity penalty if a single factor is applied generally to the entire structure when deterioration may be confined to a localized region of a single member. With the advance of time, and the need to reevaluate load capacity to account for advancing deterioration and/or increasing demands from traffic loads, future rating practices will need to adopt the Load and Resistance Factor Rating (LRFR) methodology, and rating practices will need to include &amp;#981;c and &amp;#981;s. A number of bridges clearly display significant deterioration. Steel girders are typically provided with stiffeners to prevent local yielding and instability in the web at concentrated loads, such as end reactions for simple span abutments. The stiffeners and diaphragms also provide torsional stability at the supports, to prevent roll-over of the torsionally unstable I-shaped girder cross-sections. The deterioration poses significant challenges for accurately characterizing the capacity of the structure. Local web yielding is likely to be the controlling limit state for concentrated loads on rolled sections, but web crippling may become more critical as the web becomes more slender from corrosive section loss. Losing the connection to the bottom flange will also influence the effectiveness of the diaphragm elements to provide stability and potentially redistribute loads to adjacent members. The objective of this research is to refine available &amp;#981; factors referenced in the MBE for LRFR to more reliably characterize element and system capacity and account for deterioration of structural elements in simple span steel girder bridges. The deterioration considered by the study will focus primarily on bearing conditions for simple span girders, although a range of deterioration severities and locations along spans will be considered through computational studies. Guidelines will be developed for selecting and applying appropriate &amp;#981; factors in analyses to account for deterioration of existing steel girder structures.